Code for America's open city tool NeighborDiff, powered by CartoDB, relies on local knowledge to map the evolution of Macon GA neighborhoods over five years. The project uses a shapefile from 2007 and incorporates input from neighborhood groups Habitat for Humanity and the College Hill Alliance. Users can monitor changes through a drag-and-drop interface, updating building statuses with fake click events. The goal is to create detailed maps showing current state and "diff" maps highlighting transformations, all accessible via a single table.